(1) Field of the Invention
This invention relates in general to an electrophotographic element and in particular a novel electrophotographic element comprising a charge generation layer and a charge transport layer which contains as an available ingredient at least one hydrazone compound of those having the following general formula (I): ##STR2## (where R is a hydrogen atom, a lower alkyl group, a lower alkoxyl group, a substituted or non-substituted dialkylamino group such as dimethylamino, diethylamino, ethylchloroamino or the like, halogen such as chlorine, bromine or the like, a nitro group or a hydroxyl group. n is an integer of 1-5. In case where n is 2 or more, R may be the same or different.)
(2) Description of the Prior Art
Inorganic substances such as selenium, cadmium sulfide, zinc oxide, etc. have hitherto been utilized as photoconductive materials for use in elements in electrophotographic processes. In this context, it is to be noted that the term "electrophotographic process" referred to herein generally denotes one of the image forming methods which comprise the steps of electrifying a photoconductive element in the dark first of all for instance with corona discharge or the like, then exposing the element to light in an imagewise manner to selectively dissipate the charge from only the light struck portions of the element thereby forming a latent image, and rendering the latent image visible by means of a developing process utilizing an electroscopic fine powder comprising a coloring agent called a toner, such as a dye, pigment or the like, and a binder resin such as a high molecular substance or the like, thereby forming a visible image. The element adapted for the above-mentioned electrophotographic process is required to possess the following fundamental characteristics: (1) the capability of being charged with a suitable potential in the dark, (2) low discharge rate in the dark, (3) rapid dischargeability upon light radiation and so forth. The hitherto utilized inorganic substances as enumerated above surely possess a number of merits, but at the same time possess various demerits. For instance, the now universally utilized selenium can satisfy the aforesaid requirements (1) to (3) to a sufficient degree, but is defective in that it is manufactured with difficulty and consequently the manufacturing cost is high. In addition, the selenium is defective in that it is difficult to process the selenium, which has no flexibility, into a belt, close attention must be paid in handling the selenium which is very sensitive to mechanical impact, and the like. On the other hand, cadmium sulfide and zinc oxide are utilized in the element by dispersing them in a binder resin. However, such element lacks the mechanical characteristics such as smoothness, hardness, tensile strength, frictional resistance, and therefore, as it is, can not stand repeated use.
In recent years, electrophotographic elements employing various kinds of organic substances have been proposed in order to remove the drawbacks inherent in the inorganic substances as enumerated above. Some of said elements are put to practical use, for instance, such as the element including poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-one (U.S. Pat. No. 3,484,237), the element including poly-N-vinylcarbazole sensitized with a pyrylium salt type pigment (Japanese Patent Publication No. 25658/1973), the element including an organic pigment as the principal ingredient (Japanese Laid-Open Patent Application No. 37543/1972), the element including a cocrystalline complex consisting of dye and resin as the principal ingredient (Japanese Laid-open Patent Application No. 10735/1972; etc.
As prior art relating to the elements which comprise laminating a charge transport layer on a charge generation layer using amorphous selenium or selenium alloy wherein each layer is adapted for playing its own allotted part there can be enumerated Japanese Patent Publication No. 5349/1970, Japanese Patent Publication No. 3168/1974, Japanese Patent Publication No. 14914/1975, and Japanese Patent Publication No. 10982/1976.
In addition thereto, the undermentioned elements have been developed which are prepared by laminating a charge transport layer on a charge generation layer containing a pigment of any kind. U.S. Pat. No. 3,837,851 discloses an element comprising a charge generation layer and a charge transport layer containing at least one triarylpyrazoline, U.S. Pat. No. 3,850,630 discloses an element comprising a transparent charge transport layer and a charge generation layer containing indigoid pigment, U.S. Pat. No. 3,871,882 discloses a charge generation layer containing a perylene pigment derivative and a charge transport layer containing a condensate of 3-bromopyrene and formaldehyde, and Japanese Laid-open Patent Application No. 133445/1978 discloses an element comprised of a charge generation layer containing a stilbene skeleton type disazo pigment. Some of aforesaid elements have already been put on the market, but the fact is that they do not have the various properties required for elements to a satisfactory degree.
On the other hand, it is perceivable that these excellent elements, though there are differences therebetween depending on their objects or manufacturing processes, can generally be made to exhibit superior characteristics by incorporating highly efficient photosensitive materials therein.